The major aim of this proposal is to investigate the mechanisms of mutagenesis by cyclic DNA adducts induced by metabolites of the carcinogen vinyl chloride. Our preliminary data imply that etheno-cytosine (sigma C) preferentially incorporates A residues in vivo leading to C-to-T transitions. Hydrated lesions are less mutagenic, but appear to have the same specificity. Our results point to two major categories of mechanisms for etheno adduct mutagenesis: a) Etheno lesions are essentially non-instructional in vivo. Mutagenesis opposite these lesions arises due to 'non- specific' insertion by polymerase, possibly aided by stacking interactions expected of these planar lesions. Included in this category of mechanisms is the possibility that etheno derivatives are converted to abasic sites in vivo. b) Etheno derivatives have in vivo miscoding properties which are distinct from miscoding properties observed by others in vitro. In order to test the above and other mechanisms, we propose the following experiments. 1. The effect of genetic parameters on repair and mutagenesis: specifically, the effects of RecA, SOS and excision repair. This information is essential for a more complete interpretation of our present data. 2. Response of the above genetic parameters to hydrated etheno lesions. 3. Site-specific in vivo and in vitro experiments. The in vivo experiments will confirm present sigma C data by more exacting approaches, specifically test the mutagenicity of sigma A and will test a prediction in the literature that sigma A may cause 1 bp deletions. The in vitro site-specific experiments are aimed at a more detailed understanding of events associated with bypass of sigma C and Sigma A. In addition to the above experiments, a search for E. coli N- glycosylases capable of acting on etheno lesions will be mounted in later stages. We propose to develop and use sensitive immunoassays during the course of the above studies.